Dinosaurs? & Dinosaur Warscobweb.cs.uga.edu/~maria/classes/4730-Fall-2009/slides/02-introOS-2009.pdfDinosaurs? & Dinosaur Wars No scene from prehistory is quite so vivid as that of

Maria Hybinette, UGA

CSCI 6730 / 4730 Operating Systems

Operating Systems Overview

Maria Hybinette, UGA 2

Dinosaurs? & Dinosaur Wars

No scene from prehistory is quite so vivid as that of the mortal struggles of

great beasts in the tar pits. In the mind's eye one sees dinosaurs,

mammoths, and saber toothed tigers struggling against the grip of the tar.

The fiercer the struggle, the more entangling the tar, and no beast is so

strong or so skillful but that he ultimately sinks.

Large-scale programming has over the past decade been such a tar pit, and

many great and powerful beasts have thrashed violently in it. Most have

emerged with running systems - few have met goals, schedules, and budgets.

!Frederick P. Brooks' Mythical Man-Month (1975). Description of the software

crises - likens large scale programming to a tarpit"


Evolution of our Textbook

1998 2004

2008

1983


Outline & Questions

!! What is an Operating Systems (OS)?

!! What does an OS do?

!! What is an OS and what is it not?

!! How do I run an OS?

!! How does an Operating System run?

!! What is the basic structure?

!! Computer System Component Architecture

C.R.Knight, Mural of La Brea Tar Pits. Los Angeles County Natural History Museum.!"


Questions?

!! What are the major operating system

components?

!! What are basic computer system

organizations?

!! How do you communicate with the operating

systems?

!! What services are (need to be) provided?


Poll?

!! What desktop/laptop OS do you have?

!! Which desktop/laptop OSs are you familiar

with?

!! What do you think the market share (%) is

(portion of different ODs)?


Popularity: The Desktop OS Market Share

http://en.wikipedia.org/wiki/Image:Os_as_of_2008.png Maria Hybinette, UGA

8

What is an Operating System?

!! A hardware manager

!! A program that acts as an intermediary

between a user of a computer and the computer hardware.

»! Execute user programs and make solving user

problems easier.

!! Operating system goals:

»!Make the computer system convenient to use.

»!Use the computer hardware in an efficient manner.

»!Combination of the above.

»!Handhelds (convenience), Mainframes/Servers

(efficiency)


Where is the OS? Computer System Layers

!! Hardware

!! Operating system

!! Application programs

!! Users System and Application Programs

compiler assembler text editor …

Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!

Computer system can be divided

roughly in four components:


Computer System Layers

!! Hardware:

»! provides basic computer

resources:

–! CPU, Memory, I/O Devices

System and Application Programs


Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!





!! Hardware

!! Operating system:

»! Controls and coordinates use of hardware among various applications and users.



Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!





!! Hardware

!! Operating system


»! define the ways in which the

system resources are used

to solve the computing

problems of the users

–! Word processors,

compilers, web browsers, database systems, video

games



Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!





!! Hardware

!! Operating system


!! Users

»! People, machines, other

computers



Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!





!! Hardware

!! Operating system


!! Users System and Application Programs


Operating System

Computer

Hardware

user!

1!

user!

2!

user!

n!…!




What Does Operating Systems Do?

!! A Space/Time Controller

!! It allocates resources

»!Manages all resources

»!Decides between conflicting requests for efficient

and fair resource use

!! It controls execution

»!Controls execution of programs to prevent errors

and improper use of the computer


What “Makes up” the Operating System?

!! No universally accepted definition!

!! “Everything a vendor ships when you order an operating system” used to be a good approximation… But varies wildly

!! Operating System is the “Kernel”

»! the one program that runs at all times on the computer

»! everything else is either a

–! system program (ships with the operating system) or an

–! application program


The Computer Startup Process

!! A bootstrap program (initial program) is loaded at power-up or reboot

»! Stored in firmware in ROM/EEROM

»! Stored on a chip on the motherboard (‘parentboard’)

!! Initializes all aspects of system

!! Loads operating system kernel (e.g., from disk) and starts execution

!! Pentium initial boot strap program is called the system Basic Input Output System or BIOS.


Visual of the Time-Line of the Booting Sequence

http://duartes.org/gustavo/blog/post/how-computers-boot-up

Added Slide to aid in visualizing the booting sequence - please

read the below web page for more detail (HW).


CMOS/BIOS Configuration Utility


Booting from hard disk

MBR Partition Partition Partition …

i-node i-node i-node … i-node

Boot block Super Block i-list Data blocks for files, directories, etc.

Partition Table

Free Space Management

Entire Disk:

File System:

Disk is divided into 1+ partitions: one file system per partition!


Entire Disk & Booting Computer

!! Master Boot Record (sector 0) - Pentium

»! used to boot computer

!! Partition Table

»! staring and ending address of each partition

!! “A program (e.g., the system Basic Input Output System or BIOS for Pentiums)” reads in and executes the MBR

»! searches for first active partition (noted in the partition table)

»! reads in its first block (the boot block) and executes it.

MBR Partition Partition Partition …

Partition Table


Partition Layout

!! Boot block:

»! contains a hardware specific program that is called automatically to load “UNIX” at system startup time

!! Super block:

»! file system type, #blocks in file system

!! Free space management (two lists):

»! a chain of free data block numbers

»! a chain of free i-node numbers

!! i-list/i-node table:

»! administrative information about a file (meta-data: name, type, location, size, protection bits, … ) structured into an array: inode table or simply the i-list

»! An i-node number:

–! uniquely identifies a file in a file system

–! is an index to the i-node table

Boot block Super Block i-list Data blocks for files, directories, etc.

Free Space Management


Computer System Organization

!! One or more CPUs, device controllers connect through

common bus providing access to shared memory

!! Concurrent execution of CPUs and devices competing for memory cycles


Computer System Operations

!! CPU: the processor that perform the actual computation

!! I/O controll/ers:

»! take commands in registers, generate flags and interrupts

»! each device controller

–! is in charge of a particular device type

–! has a local buffer for I/O

–! Examples: audio – output device, mouse – input, disk – I/O.

!! CPU moves data from/to main memory to/from local

buffers.

!! I/O is from the device to local buffer of controller.

!! Device controller informs CPU that it has finished its

operation by causing an interrupt.


!! How do devices communicate to the OS? For

example telling the OS to (when) check for user input?


Communication: Interrupts

!! Occurrence of an event is signaled by

interrupts either by software or hardware

»!A trap is a software-generated interrupt caused

either by an error or a user request.

!! Modern operating systems are interrupt

driven.

!! OS Stops what it is doing, preserve the

current state and then handles the interrupt (=overhead) .

An interrupt is a signal to the processor to temporarily suspend execution because some system event needs handling (alert!).


Communication: Direct Memory Access Structure

!! Used for high-speed I/O devices able to transmit information at close to memory speeds

!! Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.

!! Only one interrupt is generated per block, rather than the one interrupt per byte.

Instructions &

Data

CPU

device

DMA

instruction execution cycle & data movement

I/O request & data

& interrupt


Multi-programming

!! Single user cannot keep CPU and I/O

devices busy at all times

!! Multiprogramming organizes jobs (code and data) so CPU always has

one to execute

!! A subset of total jobs in system is kept

in memory

!! One job selected and run via job

scheduling

!! When it has to wait (for I/O for

example), OS switches to another job

Multiprogramming needed for efficiency

memory layout


User View: Timesharing (Multitasking)

!! Response time should be < 1 second

!! Each user has at least one program executing in memory !process

!! If several jobs ready to run at the same time ! CPU scheduling

!! If processes don’t fit in memory, swapping moves them in and out to run

!! Virtual memory allows execution of processes not completely in memory

Timesharing (multitasking) is logical extension in which CPU switches jobs

so frequently that users can interact with each job while it is running, creating

interactive computing


Definition of Terms

!! Uniprogramming

»! one process at the time.

!! Multiprogramming »! multiple processes (with separate address spaces) concurrently on a

machine (more on this later)

!! Multiprocessing

»! running programs on a machine with multiple processors.

!! Multithreading

»! multiple threads per address space (later).

!! Multitasking

»! a single user can run multiple processes.


Storage Structure

!! Main memory – only large storage media that the CPU

can access directly.

!! Secondary storage – extension of main memory that provides large nonvolatile storage capacity.

!! Magnetic disks – rigid metal or glass platters covered

with magnetic recording material

»! Disk surface is logically divided into tracks, which are

subdivided into sectors.

»! The disk controller determines the logical interaction

between the device and the computer.


Storage Hierarchy

!! Storage systems

organized in hierarchy.

»! Speed

»! Cost

»! Volatility

!! Caching – copying

information into faster

storage system; main

memory can be viewed as a last cache for

secondary


Performance of Various Levels of Storage

!! Putting this in perspective: Mac Book Pro 2007

!! L2 Cache – 6MB

!! Memory – 4GB (667 MHz)

!! Bus speed 800 MHz, CPU 2.6 GHz

!! Disk – 233 GB (1.5 Gigabit) Maria Hybinette, UGA

34

Caching

!! Use of high-speed memory to hold recently-accessed data.

!! Performed at many levels in a computer (in hardware, operating system, software)

!! Information in use copied from slower to faster storage temporarily

!! Faster storage (cache) checked first to determine if information is there

»! If it is, information used directly from the cache (fast)

»! If not, data copied to cache and used there

!! Cache smaller than storage being cached

»! Cache management important design problem

»! Cache size and replacement policy


Migration of Integer A from Disk to Register

!! Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy

!! Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache

!! Distributed environment situation even more complex

»! Several copies of a datum can exist

»! Various solutions covered in Chapter 17


An Operating System’s Core Tasks

!! Process Managements

!! Memory Managements

!! File Managements

!! I/O System Managements

!! Protection System


Process Management

!! A process is a program in execution (an active entity, i.e. a running program )

»! Basic unit of work on a computer

»! Examples: compilation process, word processing process

»! A process needs certain resources:

–! e.g. CPU time, memory, files, I/O devices to accomplish its task

!! Each user can run many processes at once (e.g. using &)

»! One process:

–! cat file1 file2 &

»! Two processes:

–! ls | wc -l

!! A time sharing system (such as UNIX) run several processes by multiplexing between them


Process Management Activities

!! Creating and deleting both user and system

processes

!! Suspending and resuming processes

!! Providing mechanisms for process synchronization

!! Providing mechanisms for process communication

!! Providing mechanisms for deadlock handling

The operating system is responsible for the following

activities in connection with process management:


Memory Management

!! Programs become processes when they are loaded into memory and start executing.

»! All data in memory before and after processing

»! All instructions in memory in order to execute

!! Memory management determines what is in

memory when

»! Optimizing CPU utilization and computer response to users

!! Memory management activities

»! Keeping track of which parts of memory are

currently being used and by whom

»! Deciding which processes (or parts thereof) and

data to move into and out of memory

»! Allocating and deallocating memory space as

needed

Memory Partitions

Job 1

Job 2

Job 3

Operating System


File Management

!! OS provides uniform, logical view of information storage

»! Abstracts physical properties to logical storage unit

–! A File : OS maps logical files to physical devices

»! Each medium is controlled by device (i.e., disk drive, tape drive)

–! Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random)

!! File-System management

»! Files usually organized into directories

»! Access control on most systems to determine who can access what

»! OS activities include

–! Creating and deleting files and directories

–! Primitives to manipulate files and dirs

–! Mapping files onto secondary storage

–! Backup files onto stable (non-volatile) storage media

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Mass-Storage Management

!! Main memory is volatile and limited in size

»! Use disks to store ‘overflow’ and data that needs to be persistent.

!! Disks are slower than main memory and processors

»! Entire speed of computer operation hinges on disk subsystem and its algorithms

!! OS mass storage management activities:

»! Free-space management

»! Storage allocation

»! Disk scheduling

!! Some storage need not be fast

»! Tertiary storage includes optical storage, magnetic tape

»! Still must be managed

»! Varies between WORM (write-once, read-many-times) and RW (read-write)


I/O Subsystem Management

!! One purpose of OS is to hide peculiarities of hardware

devices from the user

!! I/O subsystem responsible for

»! Memory management of I/O including

–! buffering (storing data temporarily while it is being

transferred),

–! caching (storing parts of data in faster storage for

performance),

–! spooling (the overlapping of output of one job with input of

other jobs)

»! General device-driver interface

»! Drivers for specific hardware devices


Protection and Security

!! Protection – any mechanism for controlling access of processes or users to resources defined by the OS

!! Security – defense of the system against internal and external attacks

»! Huge range, including denial-of-service, worms, viruses, identity theft, theft of service

!! Systems generally first distinguish among users, to determine who can do what

»! User identities (user IDs, security IDs) include name and associated number, one per user

»! User ID then associated with all files, processes of that user to determine access control

»! Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file

»! Privilege escalation allows user to change to effective ID with more rights


Computing Environments

!! Traditional computer

»! Blurring over time

»! Office environment

–! PCs connected to a network, terminals attached to mainframe or minicomputers providing batch and

timesharing

–! Now portals allowing networked and remote systems

access to same resources

»! Home networks

–! Used to be single system, then modems

–! Now firewalled, networked


Computing Environments (Cont.)

!! Client-Server Computing

»!Dumb terminals supplanted by smart PCs

»!Many systems now servers, responding to requests

generated by clients

–! Compute-server provides an interface to client to

request services (i.e. database)

–! File-server provides interface for clients to store and

retrieve files


Peer-to-Peer Computing

!! Another model of distributed system

!! P2P does not distinguish clients and servers

»! Instead all nodes are considered peers

»!May each act as client, server or both

!! Node must join P2P network

»!Registers its service with central lookup service on

network, or

»!Broadcast request for service and respond to

requests for service via discovery protocol

!! Examples include Napster and Gnutella


Web-Based Computing

!! Web has become ubiquitous

!! PCs most prevalent devices

!! More devices becoming networked to allow web

access

!! New category of devices to manage web traffic among

similar servers: load balancers

!! Use of operating systems like Windows 95, client-side,

have evolved into Linux and Windows XP, which can

be clients and servers


Summary

!! An Operating System (from here on OS) is a

software (a program) that performs two functions:

»! it extends the “use” of the computer hardware and

»! it manage the computer system resources

Documents

Dinosaurs? & Dinosaur Warscobweb.cs.uga.edu/~maria/classes/4730-Fall-2009/slides/02-introOS-2009.pdfDinosaurs? & Dinosaur Wars No scene from prehistory is quite so vivid as that of